Copying materials



United States Patent Office 3,549,379 Patented Dec. 22, 1970 US. Cl.96-1141 9 Claims ABSTRACT OF THE DISCLOSURE A heat-decomposable reactionproduct of an aryl thiol and a water-soluble silver salt of an inorganicoxyacid is made light-sensitive by treatment with halide ion and whenthen exposed to light is decomposable at a reduced temperature to give avisible change.

This invention is concerned with improvement in or relating to copyingmaterials. More especially the invention relates to a light sensitivecomposition which can be coated onto a suitable backing sheet and usedin the production of permanent copies of originals.

Conventional light sensitive compositions which include silver halideshave the disadvantage that when they are used to make permanent copiesof an original they require the time consuming and inconvenient steps ofWet development, wet fixing, washing and then drying. Many attempts havebeen made to obtain a light sensitive composition which after exposureto a light image gives a permanent copy with only one simple processingstep, such as heating, but no completely successful composition has beenprepared.

These difficulties are overcome to a large extent by a light sensitivecomposition in accordance with the invention which comprises a silverhalide and a silver salt of an aryl thiol (a silver mercaptide)containing an excess of silver ions in the form of an inorganic oxyacidsilver salt.

Such a light sensitive composition makes use of the known lightsensitivity of silver halides but does not have the disadvantage ofrequiring long and numerous development steps other than a simpleheating.

The silver salts used in the compositions in accordance with theinvention are decomposed by heat and this decomposition is catalyzed bythe silver halide where this has been exposed to light. It appears thatthe composition is sensitized to light of short wavelength by the silverhalide and a latent image is formed in this silver halide by the actionof light. The heating decomposes the silver salt of the aryl thiol andthe decomposition is catalyzed imagewise by the silver halide so as togive a brownishblack image. After the heat treatment causing developmentin the light-struck regions to produce a negative image, the unexposedregions are almost insensitive to light and so the image formed islargely fixed.

The silver salt of the aryl thiol containing an excess of silver ionscombined with an inorganic oxyacid is preferably prepared by reacting anaryl thiosulphuric acid having the general formula:

S SOaH any wherein Ar represents a benzene or naphthalene nucleus, andin which R represents an -NH NHR', NR'R", --OH, OR', SH or SR group,where R and R", which may be the same or different, each represent analkyl group, a substituted alkyl group, an aralkyl group or an arylgroup, or R' and R together form a ring, and R either represents ahydrogen atom or a substituent such as an alkyl or alkoxy group or ahalogen atom; with a soluble silver salt such as silver nitrate orsilver perchlorate. This silver salt should preferably be in excess toan extent of about 1.5 moles of soluble silver salt per mole of arylthiosulphuric acid.

We believe that in such a composition the excess silver ions combinedwith an inorganic oxyacid are derived from a reaction such as thatexemplified by the following equation:

Si.S 03H S A m BAgNOs H O Compositions prepared as described above aremade light sensitive by forming in the composition some silver halide.This can be accomplished, for example, by dispersing the composition inan aqueous medium containing a. water soluble binder, such for exampleas, polyvinyl alcohol, polyvinyl alcohol/acetate copolymer or polyvinylpyrrolidone, and adding a water soluble halide, eg a potassium orcadmium halide.

These light sensitive compositions are particularly sensitive to ultraviolet and blue light but the sensitivity can be extended to longerwavelengths by the addition of spectral sensitizers such for example asthe cyanine and merocyanine types of dye.

The light sensitive compositions can be used in the form of a coating ona backing sheet of, for example, paper or plastic film.

The invention will now be described with reference to the followingexamples.

EXAMPLE 1 S-Z-aminophenyl thiosulfuric acid (0.66 gram mole) wasdissolved in 3 litres of distilled water at C. 700 ml. of an aqueoussilver nitrate solution containing 1 gram mole of silver nitrate wasthen run into the stirred solution of the acid during a period of eightminutes. The yellow precipitate formed was allowed to stand for twelvehours. filtered, washed with water and dried.

10 g. of the above silver salt was ball milled for sixteen hours withml. of a 5% aqueous solution of Gelvatol 40/20 a water-soluble polyvinylalcohol/acetate copolymer formed by partial hydrolysis of polyvinylacetate, containing 37-42% residual unhydrolyzed ester, having aviscosity, as a 4% solution in water, of 2-3 centipoise, and having anapproximate weight average molecular weight of 3000. The resultantdispersion was stirred and 20 ml. of a 0.42 molar aqueous potassiumbromide solution was added to'make the composition light sensitive.After continued stirring for one hour the dispersion was coated onto apaper base and air dried. Suitable coating weights were found to bewithin the range of approximately 5 to 100 mg. of silver per squaredecimeter.

The coating so prepared was exposed through a negative held in contactwith it to tungsten light for 10 meter candle seconds and wassubsequently developed by holding in contact with a heatedsmooth-surfaced copper cylinder at C. for ten seconds. A black-brownimage of the negative on a substantially light insensitive pale yellowbackground was thereby produced.

EXAMPLE 2 10 g. of the silver salt prepared as in Example 1 was ballmilled for sixteen hours with 100 ml. of a 5% aqueous solution ofpolyvinyl alcohol/ acetate copolymer. The resultant dispersion wasstirred and 7 ml. of a 0.42 M

+ AgzSO; BHNOs EXAMPLE 3 To a stirred solution of 3.1 .g. ofS-2-aminophenyl thiosulphuric acid in 100 ml. of water was added asolution of 6.2 g. of silver perchlorate in 20 ml. of water. Afterstirring for three minutes, the yellow precipitate so formed wasfiltered off, well washed with water and dried at 50 C.

10 g. of the silver salt prepared by the above procedure was dispersedin 100 ml. of a 5% aqueous solution of water-soluble polyvinylalcohol/acetate copolymer by ball milling for 16 hours. The resultantdispersion was sensitized to light by the addition of 20 ml. of 0.42 Maqueous potassium bromide solution. After stirring for one hour thedispersion was coated onto paper base and dried.

The coating so prepared Was exposed through a negative to meter candleseconds of tungsten light followed by development at 175 C. Abrown-black positive image was formed on a substantially lightinsensitive pale yellow background.

EXAMPLE 4 10 g. of the yellow precipitate prepared as in Example 1 wereball milled for 16 hours with 100 ml. of a 5% aqueous solution of apolyvinyl alcohol/acetate copolymer (Gelvatol 40/20). The resunltantdispersion was stirred and 20 ml. of 0.42 M aqueous potassium chloridesolution were added. After continued stirring for 45 minutes, thedispersion was coated onto paper base and dried. Exposure of the coatingthrough a negative to tungsten light for 10 metre candle secondsfollowed by development at 175 C. for 10 seconds gave a brown-blackpositive image on a pale yellow background.

EXAMPLE 5 2.5 g. of the yellow precipitate prepared as in Example 1 wereball milled for 16 hours with ml. of a 5% aqueous solution of polyvinylalcohol/ acetate copolymer (Gelvatol /20). The resultant dispersion wasstirred and 2.5 ml. of a 0.42 M aqueous potassium bromide solution wereadded, followed by 4 ml. of a 0.001 molar aqueous solution of thefollowing merocyanine dye:

v After stirring for 5 minutes the dispersion was coated onto paper baseand dried.

Exposure of such a sheet to white light behind a nega- 4 tive and aseries of narrow cut spectral filters followed by 'development at C. for10 seconds showed an extended photographic response into the greenregion of the spectrum.

It will be apparent from the above examples that the light sensitivecompositions and coatings, prepared in accordance with the invention,yield an image which is largely fixed by the simple step of heating thecoating after it has been exposed to a light image; such time consumingsteps as wet development, wet fixing, washing and drying are notrequired.

What we claim is: I

1. A light-sensitive composition formed by a process comprising mixingtogether aqueous solutions of S-2- aminophenylthiosulfuric acid and ofsoluble silver salt to form a silver-containing heat-decomposableprecipitate, and treating said precipitate with halide ion.

2. Composition of claim 1 wherein the molar ratio of saidS-2-aminophenylthiosulfuric acid and said soluble silver salt is between111.5 and 1:3.

3. Composition of claim 1 wherein the precipitate is treated in aqueoussuspension by addition of a Watersoluble halide.

4. Composition of claim 1 wherein said soluble silver salt is silvernitrate or silver perchlorate.

5. Composition of claim 1 wherein is included a cyanine or merocyaninespectral sensitizer dye.

6. Sheet material capable of exhibiting a stable visible image onexposure to a light-image followed by heating, said sheet materialcomprising a backing having over one surface thereof the dried residueof a coating of the composition of claim 1 in which is included abinder.

7. Sheet material capable of exhibiting a stable visible image onexposure to a light-image followed by heating, said sheet materialcomprising a backing having over one surface thereof the dried residueof a coating of the composition of claim 5 in which is included abinder.

8. Method of producing a visible image comprising exposing a sheetmaterialas defined in claim 6 to a lightimage having a radiant energywithin the range including visible and ultraviolet light and heating theexposed sheet to a temperature and for a time sufficient to develop acorresponding visible image.

9. A method of producing a visible image comprising exposing a sheetmaterial as defined in claim 7 to a light image having radiant energywithin the range including visible and ultraviolet light and heating theexposed sheet to a temperature and for a time sufficient to develop acorresponding visible image.

References Cited UNITED STATES PATENTS 3,155,507 11/1964 Blake 96943,206,309 9/1965 Haist 9694 3,384,485 5/1968 Blake 96-94 NORMAN G.TORCHIN, Primary Examiner M. KELLEY, Assistant Examiner US. Cl. X.R. 96114.6

